This research focuses on selected determinants of changes in sexual behavior and contraceptive use for adolescent girls and boys. Attention is concentrated on the socialization processes through which these youth develop attitudes toward heterosexual behavior and the ways in which these attitudes as well as situational opportunities to engage in heterosexual behavior produce variations in patterns of heterosexual interaction during the adolescent years. The research is guided by an analytic model of the stages of heterosexual behavior which include: (1) cross-sex friendships, (2) dating, (3) sexual play, (4) coitus without contraception, and (5) coitus with contraception. Behavior within these stages, as well as the probability of transition from one stage to another, is hypothesized to result most directly from the interaction of the adolescent's attitudes and opportunities related to heterosexual conduct. Adolescent attitudes are a function of internalized norms and beliefs, which stem from norms and beliefs transmitted through socialization processes as well as from the adolescent's idiosyncratic perceptions and experiences. Opportunities to engage in heterosexual behavior are determined by the interaction of several factors, primarily constraints imposed by interpersonal relationships and temporal and locational settings. The study design incorporated longitudinal as well as cross-sectional procedures. The longitudinal component will be focused on adolescents 12 through 15 years of age at the beginning of the study. Interviews will be conducted annually over a three-year period with the adolescents, their parents, one same-sex friend, and one cross-sex friend. Cross-sectional comparisons will be amplified through the inclusion of a sample of 16/17-year-old youth during the first year of the study and a new sample of 12/13-year-olds during the third year. The first round of interviews is nearing completion. By including parents and peers in addition to the adolescents, we will provide a "triangulated" perspective on the influences and processes through which sexual attitudes and opportunities are developed and the conditions under which patterns of heterosexual behavior are formed and undergo change.